Thermally-operable circuit breaker



1966 R. A. JOHNSON 3,265,839

I THERMALLY-OPERABLE CIRCUIT BREAKER Filed Aug. 5, 1963 Llllllllllll:lllllll:l I'll T INVENTOR. ROBERT A. JOHNSON BY Z United StatesPatent New York Filed Aug. 5, 1963, Ser. No. 299,940

2 Claims. (Cl. 2t)0122) This invention relates to circuit breakers, and,more particularly, to automatically resetting circuit breakers forautomotive use, for protecting automotive electrical systems.

Automatically resetting circuit breakers are in wide use particularly inthe electrical systems of automotive vehicles and the like. However,when used in automotive electrical systems, the conventional circuitbreakerhas a limited life because of the arcing conditions that exist inDC. circuits with the slow make and break type of devices conventionallyemployed. Moreover, with conventional circuit breakers a rather hightemperature is necessary to maintain an open circuit. Furthermore,ordinarily, when a circuit overload condition develops, the circuitbreaker recycles continuously until either the vehicles battery runsdown, or the overload condition is corrected. In the case of an overloadcaused by a short circuit, for example, such action not only places arelatively heavy drain upon the battery, but also constitutes a firehazard because of the relatively heavy electrical currents in thewiring.

One important object of the present invention is to provide a novelcircuit breaker including means operative after a few recyclingoperations-of the circuit breaker due to an overload condition in theload circuit either to hold the breaker open until the load circuit iselectrically removed, or to increase the reset time on subsequent cyclesof operation whereby the hereinabove noted disadvantages of prior artautomatically resetting circuit breakers are avoided.

Another object of the invention is to provide a circuit breaker that'will have an extended life as compared to conventional slow make andbreak circuit breakers employed in automotive circuits.

Another object of the invention is to provide a circuit breaker thatwill operate in a DC. circuit with a snap action movement whenseparating the contacts.

Another object of the invention is to provide a circuit breaker than canbe adjusted to initial surge currents, or temporary overloads of shortduration, without permanently disrupting the operation of circuits, byacting as a normal automatic reset breaker.

Still another object of the invention is to provide a snap-actioncircuit breaker with which the effective current, that is allowed topass, is held to a minimum, thereby offering the utmost in circuitprotection.

A still further object of the invention is to provide a snap-actioncircuit breaker that remains in open position at a lower temperaturethan that required to maintain an open circuit with a slow make andbreak circuit breaker.

Other objects and advantages of the invention will become apparent fromthe following detailed description of representative embodimentsthereof, and from the recital of the appended claims, particularly whentaken in conjunction with the drawing, wherein:

FIG. 1 is a plan view of a circuit breaker made according to a firstembodiment of the present invention, the circuit breaker being shownwith its cover removed;

FIG. 2 is a side elevational view of the circuit breaker of FIG. 1;

FIG. 3 is a cross-sectional view on an enlarged scale taken along theline 33 of FIG. 1;

FIG. 4 is a plan view of a circuit breaker made ac- Patented August 9,1966 cording to a second embodiment of the invention, the circuitbreaker again being shown with its cover removed; and

FIG. 5 is a schematic circuit diagram illustrating how circuit breakersmade according to the present invention may be connected in circuit.

Briefly, the invention contemplates connecting a Joulcan heating elementacross the contacts of a conventional circuit breaker of the thermallyresponsive, auto matically resetting type, and mounting the heatingelement adjacent to the armature of the circuit breaker. The value ofthe heating element is chosen so that when a circuit overload conditionsuch as a short-circuit occurs, it will, after a relatively fewrecycling operations of the armature, produce sufficient heat either tokeep the armature open, or to delay its reclosing on each subsequentcycle so that the average power delivered to the load circuit may bereadily dissipated by ambient cooling. During times when the circuitbreaker contacts are open, the heating element limits the currentflowing into the load circuit to a very low value.

For purposes of convenient reference herein, the type of operation inwhich the heating element maintains the armature in its open positionuntil the load circuit is substantially completely disconnected from thecircuit breaker will be referred to as a remote reset type of operation,and the type of operation in which the reset period of the circuitbreaker is prolonged will be referred to as the delayed reset type.

Referring now to the drawing, the circuit breaker shown in FIGS. 1, 2,and 3 is of the remote resetting type, although, of course, by properchoice of the values of the heating elements, 10 and 12, it may beconverted to a delayed resetting type.

The device includes a conventional body member 14, which may be, forexample, of a molded plastic material. A pair of studs 16 and 18 extendthrough the body 14 for connecting the device to an external circuit. Afixed contact 20 is welded, or otherwise securely attached to one end ofright hand stud 18; and a bimetallic, thermally reacting conductiveanmature 22 is cantilevered on the other stud 16, with its free endextending over the fixed contact 20. The armature 22 is secured to stud16 by welding or by a headed stud or screw 23.

The movable contact 24 is fixed on the free end of the armature orswitch blade 22, and is normally held in pressure engagement with thefixed contact 20 by the armature or switch blade. The armature or switchblade 22 is preferably of the snap-action type such as the armatures orswitch blades shown in US. Patents 2,533,274, Matulaitis et al., and2,425,717, Bean. Thus, the armature or switch blade 22 shown has slots25 therein whose adjacent sides converge toward the fixed end of theblade, and cars 27 along the distal, generally parallel sides of theslots, which protrude both into the slots and from the longitudinalsides of the blades.

The circuit breaker of FIGS. 1 to 3 inclusive is made to operate in theremote resetting mode by connecting a pair of resistors 10 and 12 inparallel with armature blade 22 between the studs 16 and 18 closelyadjacent to the armature 22 so that when an overload condition developsin the load circuit, they will conduct current and heat the armature 22while the armature is in its open position. For convenience in assemblyand for added rigidity of construction, the body 14 is provided withside and end walls 26 and 28, which extend from the main portion of thebody upwardly and define a recess 30 for receiving the resistors 10 and12 and holding them snugly against the studs 16 and 18. The resistors 10and 12 constitute an electrical connection between the two studs 16 and18in parallel with the connection afforded through the armature 22 andthe contacts 20 and 24, as schematically shown in FIG. 5. A cover (notshown) may be provided, if desired, fitting over the armature andsealing upon the body 14 to protect the contacts 20 and 22 from dust andother environmental effects.

The values of the resistors 19 and 12 are so chosen that in operation,when a short circuit develops in the load circuit, the resistors willdevelop sufficient heat-to prevent In an ordinary automobile thearmature 22 from closing. type circuit breaker, for example, designed tooperate in a 12 volt electrical system, in which the armature 22 isadapted to reset when at a temperature of between about 200 F. and 180F., and which is provided with a sheet metal cover, it has been foundthat the remote reset type of operation is obtained when the resistorsand 12 have values of about 40 ohms each, making a net resistance of 20ohms. Different values will be required for use in circuit breakershaving other operating characteristics and specifications.

In operation under normal conditions, the resistors 10 and 12 havesubstantially no effect on the circuit breaker, or on the load circuit,because their resistance is many times higher than the resistance of thearmature 22 in series with the contacts 21] and 24. In a parallelcircuit current flows through the path of least resistance. The resistorvalue is higher than the bi-metallic blade resistance by a ratio thatallows only a minute portion of current to flow through the resistorsuntil such time that an overload condition causes the bi-metallic bladeto open that part of the circuit, which then allows the resistors toheat to the point where they will keep the blade 22 open. When anoverload condition such as a short circuit develops, the resistors 10and 12 still have no effect until after the-armature 22 opens. They donot operate to delay opening of the armature to any appreciable extent.As soon as the armature opens, the full electrical supply voltage,assuming a short circuit in the load circuit, ap-

pears across the two resistors 10 and 12 in parallel, and they begin toproduce heat. The temperature of the resistors 10 and 12 increasesrelatively slowly so that the first two or three recycling operations ofthe armature 22 are at a rate relatively close to its normal rate ofrecycling, that is, relatively close to the rate at which it wouldrecycle if the resistors 10 and 12 were removed from the device.Thereafter, the resistors 10 and 12 become warm enough to hold thetemperature of the armature 22 above its reset temperature, therebyholding the armature open and preventing it from closing until such timeas the flow of energizing current through the resistors 10 and 12 isstopped, such as by opening the load circuit. The resistors hold theblade 22 open because they produce an ambient temperature around theblade which is in excess of the temperature that would have permittedthe blade to reset had the resistors not been present. The resistors 10and 12 allow a relatively small current of less than 1 ampere to flow inthe load circuit during the existence of the overload condition, whichcurrent is insufficient to present a fire hazard under most conditionsand will not rapidly drain the vehicles battery 32 (FIG. 5).

A delayed reset type of circuit breaker according to an alternativemodification of the invention is shown in FIG. 4, and is generallysimilar to the circuit breaker shown in FIGS. 1 to 3, except that itincludes only one resistor 10 connected between the terminal studs (notshown in FIG. 4). The armature or switch blade 42 is here alsobimetallic and of the snap action type but its longitudinal sides areparallel as are the adjacent sides of the slots 45 formed therein. Thedistal sides of the slots have, however, lobes 47 formed thereonextending toward one another.

In the delayed reset type of device shown in FIG. 4, when an overloadcondition first arises in the load circuit, the armature 42 recyclesthree or four times at a rate close to its normal recycling rate, butthereafter its resetting time becomes greatly extended due to the risein temperasuch that the average power delivered to the load circuit amay be'dissipatedwithout fire hazard and is insufficient to cause arapid exhaustion of the battery 32 (FIG. 5).

The inclusion of the resistors, or heating elements 10 and 12 accordingto the invention has substantially no effect on the initial openingcharacteristics of the circuit breakers, and therefore permits theutilization of the advantageous snap-action type of armature. Becausethe circuit breakers can open and reset several times on overload,before the heating elements become warm enough to have a significanteffect, the circuit breakers may be subjected to initial surge currentsor temporary overloads of short duration, acting otherwise asconventional, automatically resetting circuit breakers. However, whenthe circuit overload condition persists, the circuit breakers of theinvention will then function in either the delayed reset or remote resetmode.

The remote reset device requires that the circuit be disconnectedelectrically, external to the circuit breaker,

by means of a switch or some device which limits or stops the flow ofcurrent through the resistors. The delayed reset type of device extendsthe reset time beyond that which would normally be inherent to thebreaker; the result is a reduction in the effective value of currentthatthe circuit breaker will allow to pass over an extended period of time.The remote reset type will completely stop the overloaded valueofcurrent from flowing. Moreover, because a'circuit breaker madeaccording to the invention will trip and recycle far fewer times duringthe existence of an overload condition than a conventional circuitbreaker, the life of the circuit breaker and its contacts is greatlyextended relative to circuit breakers of previously known types.

be lower than the temperature that is necessary to main tain an opencircuit on a slow make and break circuit breaker. This is an addedadvantage in a circuit breaker made according to the present invention.

While the remote reset type circuit breaker shown uses two resistors,and this type of circuit breaker may be converted to a delayed resettype by removing one resistor, it will be obvious that it is possible tobuild the delayed reset type with any resistor or with a pair ofresistors, selected to generate the desired resistance. Obviously it isalso possible to build the remote reset type circuit breaker by usingonly a single resistor whose resistance is low enough to cause thebi-metallic armature to remain open as long as voltage is applied.

While the invention has been described in connection with a specificembodiment thereof, then, it will be under- In both the remote reset andthe delayed reset type of operation, the effective current Having thusdescribed my invention, what I claim is:

1. A circuit breaker comprising (a) a pair of contacts adapted to beconnected to an external electric circuit,

(b) a bimetallic, electrically-conducting snap-action blade cantileveredat one end on one of said contacts and having its free end positioned toengage the other contact, said blade being responsive to current flowingtherethrough to heat and to snap out of engagement with said othercontact when heated beyond a predetermined degree and said blade beingconstructed to reengage said other contact when said blade cools belowsaid predetermined degree, and

(c) a resistance connected continuously at opposite ends to saidcontacts in parallelism with and spaced from said blade when said bladeis in its engaged, closed position,

(d) the value of the resistance being many times higher I than that ofsaid blade, whereby said blade will make and break the circuit throughsaid blade under normal circuit loads, said resistance being adapted toheat up when an overload occurs in the circuit and being disposed closeenough to said blade to heat said blade and to maintain said blade inits open position when an overload persists.

2. An automatically resetting, electric circuit breaker having a pair ofcontacts, a snap-action bimetallic armature electrically connected inseries with the contacts for alternately opening and closing them inaccordance with the heat produced in the armature by current flowingthrough it, a Joulean heating element continuously connected across thecontacts in parallelism with said armature and mounted adjacent to butspaced from the armature for heating it during times when the contactsare held in their open position by the armature, whereby the reset timeof the circuit breaker is lengthened, the value of said heating elementbeing chosen in view of the supply voltage of the system in which it isintended for use and in view of the operating characteristics of thearmature so that in service when a short circuit occurs in the loadcircuit said heating element will heat the armature sufficiently toprevent its reclosing once thermal equilibrium is established.

References Cited by the Examiner UNITED STATES PATENTS 1,701,757 2/1929Lea 200-122 2,403,803 7/1946 Kearsley 200-138.6 2,884,501 4/1959 Dorian200l 38.6 2,914,637 11/1959 Wuerth 200-122 3,141,080 7/1964 Ege 200113.7

FOREIGN PATENTS 677,161 8/1952 Great Britain.

BERNARD A. GILHEANY, Primary Examienr. L. A. WRIGHT, Assistant Examiner.

2. AN AUTOMATICALLY RESETTING, ELECTRIC CIRCUIT BREAKER HAVING A PAIR OFCONTACTS, A SNAP-ACTION BIMETALLIC ARMATURE ELECTRICALLY CONNECTED INSERIES WITH THE CONTACTS FOR ALTERNATELY OPENING AND CLOSING THEM INACCORDANCE WITH THE HEAT PRODUCED IN THE ARMATURE BY CURRENT FLOWINGTHROUGH IT, A JOULEAN HEATING ELEMENT CONTINUOUSLY CONNECTED ACROSS THECONTACTS IN PARALLELISM WITH SAID ARMATURE AND MOUNTED ADJACENT TO BUTSPACED FROM THE ARMATURE FOR HEATING IT DURING TIMES WHEN THE CONTACTSARE HELD IN THEIR OPEN POSITION BY THE ARMATURE, WHEREBY THE RESET TIMEOF THE CIRCUIT BREAKER IS LENGTHENED, THE VALUE OF SAID HEATING ELEMENTBEING CHOSEN IN VIEW OF THE SUPPLY VOLTAGE OF THE SYSTEM IN WHICH IT ISINTENDED FOR USE AND IN VIEW OF THE OPERATING CHARACTERISTICS OF THEARMATURE SO THAT IN SERVICE WHEN A SHORT CIRCUIT OCCURS IN THE LOADCIRCUIT SAID HEATING ELEMENT WILL HEAT THE ARMATURE SUFFICIENTLY TOPREVENT ITS RECLOSING ONCE THERMAL EQUILIBRIUM IS ESTABLISHED.